At the end of the fourteenth century John VI. asked for efficient military aid from Western Europe to avert the overthrow of the Greek Empire by the Othoman power, but the Pope refused, unless John consented to the union of the Greek and Latin Churches and the recognition of the papal supremacy. In 1438 the Council of Ferrara was held, and was transferred in the following year to Florence, when the Greek emperor and all the bishops of the Eastern Church, except the bishop of Ephesus, adopted the doctrines of the Roman Church, accepted the papal supremacy, and the union of the two Churches was solemnly ratified in the cathedral of Florence on July 6, 1439. But little came of the union. The Pope forgot to sent a fleet to defend Constantinople; the Christian princes would not fight the battles of the Greeks. Then followed the conquest, in May 1453, of Constantinople, despite a desperate resistance, by Mohammed II., who entered his new capital, riding triumphantly past the body of the Emperor Constantine. Mohammed proceeded at once to the church of St. Sophia, where, to convince the Greeks that their Orthodox empire was extinct, the sultan ordered a moolah to ascend the Bema and address a sermon to the Mussulmans announcing that St. Sophia was now a mosque set apart for the prayers of true believers. The fall of Constantinople is a dark chapter in the annals of Christianity. The death of the unfortunate Constantine, neglected by the Catholics and deserted by the Orthodox, alone gave dignity to the final catastrophe. _III.--Othoman and Venetian_ The conquest of Greece by Mohammed II. was felt to be a boon by the greater part of the population. The sultan's government put an end to the injustices of the Greek emperors and the Frank princes, dukes, and signors who for two centuries had rendered Greece the scene of incessant civil wars and odious oppression, and whose rapacity impoverished and depopulated the country. The Othoman system of administration was immediately organised. Along with it the sultan imposed a tribute of a fifth of the male children of his Christian subjects as a part of that tribute which the Koran declared was the lawful price of toleration to those who refused to embrace Islam. Under these measures the last traces of the former political institutions and legal administration of Greece were swept away. The mass of the Christian population engaged in agricultural operations were, however, allowed to enjoy a far larger portion of the fruits of their labour under the sultan's government than under that of many Christian monarchs. The weak spots in the Othoman government were the administration of justice and of finance. The naval conquests of the Othomans in the islands and maritime districts of Greece, and the ravages of Corsairs in the sixteenth and seventeenth centuries, reduced and degraded the population, exterminated the best families, enslaved the remnant, and destroyed the prosperity of Greek trade and commerce.